Improved Cycle Properties of All-Solid-State Li-Ion Batteries with Al2O3 Coating on the Silicon-Based Anode

Abstract

The demand for the development of high-capacity, safe, and long-life secondary batteries and the interest in all-solid-state batteries are increasing. The cycle performance of solid-state batteries is limited by interfacial phenomena at the electrolyte–anode interface hindering the ion diffusions. A multifunctional aluminum oxide (specifically, Al2O3) coating was created for application on silicon-based anodes in all-solid-state lithium-ion batteries. In an all-solid-state lithium-ion battery, the electrochemical properties of Al2O3 coating were enhanced. The coating was applied to provide stable artificial solid electrolyte interphase (SEI) layers on the silicon-based anodes. Al2O3 layers not only promote the diffusion of Li+ through the Li–Al–O, but their intrinsically low electronic conductivity also limits the transmission of electrons at the contact between the anode and the electrolyte. A Si alloy–polyacrylonitrile anode was prepared using Al2O3 coating as an artificial SEI layer by radio-frequency (RF) plasma. Radio-frequency sputtering was used to create a simple and economical Al2O3 coating. The cycle properties of silicon-based anodes were enhanced by the addition of the thin amorphous aluminum oxide layer (i.e., Al2O3 coating). After 100 charge–discharge cycles, the half-cell with the Al2O3 layer delivered a discharge capacity of 502.08 mAh g−1 and a capacity retention ratio of 58.86%. After 100 cycles, the sample without the Al2O3 layer had a discharge capacity of 278.48 mAh g−1 and capacity retention of 34.34%. Cells with an Al2O3-coated anode retained high capacity after 100 cycles. Thus, the Al2O3-coated Si-based anodes were cycled successfully in all-solid-state half-cells to produce functional high-performance lithium-ion batteries. In this study, we employed the vacuum deposition method, radio-frequency sputtering, to deposit very thin layer of aluminum oxide on the surface of fully fabricated anodes for improved cycling properties of all solid-state battery. This layer of aluminum oxide was confirmed using advanced elemental analysis techniques. The aluminum oxide layer with 1-min coating had much-improved cycling characteristics compared with those of the sample with no coatings. Previous studies have used theoretical calculations to report that an aluminum oxide coating layer improves the stability characteristics for sulfide-based solid electrolytes. In this paper, the actual stability improvement of the sulfide-based solid electrolyte was demonstrated in terms of much improved cycling characteristics throughout the cycling test. The appropriate amount of aluminum oxide coating decreases the decomposition of solid electrolyte and also decreases the consumption of Li ions during lithiation and delithiation. This surface modification technique can be utilized to improve the cycling stability of solid-state batteries, which is one of the critical factors for the early adoption of solid-state batteries for electric vehicle applications.